This invention relates to coloring matter for a filter for electronic display devices and a filter containing the coloring matter for display panels. More particularly, the invention relates to a specific squarylium dye and a display filter containing the same which is capable of controlling the tone of an electronic display device or increasing the purity of luminescence color without reducing the luminescence intensity of the display device.
Color display devices hitherto developed include CRTs, vacuum fluorescent tubes, field-emission displays, plasma display panels (PDPs), liquid crystal displays, and electroluminescence displays. In these display devices, an image is displayed by combinations of luminescence of three primary colors, red, green and blue. In order to obtain a clear color image with corrected color balance, it is necessary to use a so-called band pass filter which can absorb unnecessary luminescence other than the three primary colors. Various band pass filters containing coloring matter have been studied for this use. It is important for the coloring matter used in the band pass filters to have no absorptions other than a desired absorption and to have sufficient resistance to heat and light.
Known color correction filters for displays include those containing commercially available coloring matter which selectively absorbs light of specific wavelengths, as disclosed, e.g., in JP-A-61-188501, JP-A-10-26704, WO98/57201, WO98/23980, and WO99/1983. The problem of these conventional color correction methods lies in that the filter absorbs part of necessary components of the three primary colors only to impair the color balance or to darken the display.
An antireflective film containing a squarylium compound has recently been proposed as disclosed, e.g., in JP-A-2000-43175. However, the disclosure does not refer to a dipyrazolylsquarylium compound as a specific example of the squarylium compound nor the correlation between the compound structure and a light transmission at various wavelengths.
With reference to pyrazolylsquarylium compounds, Angew. Chem. Internat. Edit., vol. 7, p. 530 (1968) describes that an N-phenyl dipyrazolylsquarylium compound is an orange color but has no mention of the absorption spectral wave form, etc. of the compound.
U.S. Pat. No. 4,175,956 discloses an N-phenyl dipyrazolylsquarylium compound as a red color useful as an electrophotographic photoreceptor without referring to the transmissions at various wavelengths.
An object of the present invention is to provide coloring matter for display filters, which has a transmission spectrum having a sharp minimum value in a wavelength region of from 480 to 520 nm and which is therefore capable of selectively cutting light of wavelengths t the valley between blue and green.
Another object of the present invention is to provide a display filter, such as a color correction filter, a color purity improving filter, and a color reproduction range broadening filter, which performs the desired function without adversely affecting luminescence of the three primary colors, red, blue and green.
As a result of extensive investigation, the present inventors have found that the above objects of the invention are accomplished by a specific squarylium dye having a pyrazolyl group.
The present invention provides:
coloring matter for a filter of a display device which comprises a dipyrazolylsquarylium compound represented by formula (I): 
wherein A and B each independently represent a substituted or unsubstituted pyrazolyl group;
a display filter containing the coloring matter; and
a squarylium compound represented by formula (II): 
wherein R1 represents a substituted or unsubstituted alkyl group; R2 represents a substituted or unsubstituted alkyl group or a substituted or unsubstituted aryl group; and R1 and R2 may be the same or different.
The filter according to the present invention exhibit s excellent durability, such as heat resistance and light resistance, and gives no adverse influences on luminescence of the three primary colors.